电气原理基础知识自学手册【中英】PPT课件

.,1,电气原理基础知识BasicKnowledgeofElectricalPrinciples,中联重科工程起重机分公司ZoomlionMobileCraneBranchCompany,2013.04April2013,.,2,3、汽车起重机电气符号认识KnowledgeofElectricalSymbolsofAutomobileCrane,目录Contents,1、电路模型CircuitModel,2、电路原理PrincipleofCircuits,.,3,电路Circuit,电路就是由一些电器设备和电子元器件组成的电流流通的闭合路径。Acircuitisaclosedpathcomposedofafewelectricalequipmentandelectronicpartsandcomponentsforcurrentflow.随着科学技术的进步，电的应用越来越广泛，电路的形式更是多种多样。但是不论电路的具体形式和复杂程度初何变化，它们都是由一些最基本的部件组成的。以最常见的手电筒电路为例，其电路示意如图。Withthedevelopmentofscienceandtechnology,electricityisappliedincreasinglyandtheformsofcircuitsarealsodiverse.However,nomatterhowthespecificformsandcomplexityofcircuitschange,thecircuitsarecomposedofthemostbasiccomponents.Takingthemostcommonflashlightcircuitasanexample,theschematicdiagramofitscircuitisasfollows:,电路的组成Compositionofthecircuit,电源：它把其他形式的能量转换成为电能，是电路中电能的来源。例如干电池将化学能转换成电能，发电机将机械能转换成为电能等。电源在电路中起激励作用，在它的作用下产生电流与电压。Powersupply:Itisusedtoconvertenergyofotherformsintoelectricalenergyanditisthesourceofelectricalenergyinthecircuit.Forexample,adrybatteryconvertschemicalenergyintoelectricalenergyandanelectricgeneratorconvertsmechanicalenergyintoelectricalenergy.Thepowersupplyactsinincentivefunctioninthecircuitandcurrentandvoltagewillbegeneratedunderitseffect.负载：它是电路中的用电设备，它把电能转换成为其他形式的能量。例如白炽灯将电能转换成为热能和光能，电动机将电能转换成为机械能等。Load:Itisanelectricequipmentinthecircuitandconvertselectricalenergyintoenergyofotherforms.Forexample,anincandescentlightbulbconvertselectricalenergyintothermalenergyandopticalenergy;andamotorconvertselectricalenergyintomechanicalenergy.中间环节：指连接导线和控制电路通、断的开关电器，它们将电源和负载连接起来形成电流通路。中间环节还包括保证安全用电的保护电器（如熔断器）等。Intermediatelink:Itcomprisesaconnectingwireandaswitchingdeviceforcontrollingconnectionanddisconnectionofthecircuit.Theyareusedtoconnectthepowersupplytotheloadtoformacurrentpath.Theintermediatelinkfurthercomprisesaprotectiondevice(suchasafuse)forensuringsafetyutilizationofelectricpower.,.,4,电路模型CircuitModel,实际使用的电路都是由各样的元器件组成，不同的元器件具有不同的电磁性质、电阻性。除此之外，电流通过电阻产生磁场，具有电感性。产生电场，当电流流过其他电工设备和电子元器件时，所发生的电磁现象与此大体相同，都是十分复杂的。如果把所有这些电磁特性全都考虑进去，会使电路的分析与计算变得非常繁琐，甚至难于进行。Thecircuitinpracticaluseiscomposedofvariouspartsandcomponentsandvariouspartsandcomponentshavevariouselectromagneticpropertiesandresistances.Inaddition,thecurrentgeneratesamagneticfieldthroughresistance.Themagneticfieldhasaninductivecharacter,soastogenerateanelectricfield.Whenthecurrentflowsthroughotherelectricalequipmentandelectronicpartsandcomponents,theoccurringelectromagneticphenomenonisgenerallythesameasthiswhichisquitecomplicated.Iftakingalltheseelectromagneticpropertiesintoconsideration,analysisandcalculationofthecircuitwillbecomequitecomplicatedorevenbehardtobecarriedout.所以，忽略实际电工设备和电子元器件的一些次要性质，只保留它的一个主要性质，并用一个足以反映该主要性质的模型理想化电路元件来表示。Therefor,ignoresomesecondarycharactersoftheactualelectricalequipmentandelectronicpartsandcomponents,onlyreserveamaincharacterandrepresentwithamodel-idealisticcircuitcomponentswhichcanfullyreflectthismaincharacter.,电流Current,1.电流的形成：带电微粒有规则的定向运动形成电流。Currentgeneration:Currentisgeneratedthroughregulardirectionalmovementofchargedcorpuscles.2.电流的大小：在直流电路中，电流的方向和大小都不随时间变化。假设在t时间内，通过导体横截面的电荷量是Q，则电流用I表示为：Currentmagnitude:InaDCcurrent,thedirectionandmagnitudeofcurrentwillnotchangewithtime.AssumingthatthequantityofelectricchargepassingthroughthecrosssectionofaconductorwiththetimeoftisQ,thecurrentIisrepresentedbythefollowingformula:,在国际单位制中，电荷Q的单位是库（仑）（C），时间t的单位是秒（S），电流I的单位是安(培)（A）。IntheInternationalSystemofUnits,theunitsofelectricchargeQ,timetandcurrentIarecoulomb(C),second(S)andampere(A)respectively.,.,5,电压Voltage,电压的定义Definitionofvoltage电压是衡量电场力推动正电荷运动，对电荷做功能力的物理量。电路中AB两点之间的电压在数值上等于电场力把单位正电荷从A点移动到B点所做的功。若电场力移动的电荷量是Q，所做的功是W，则两点间的电压为Voltageisaphysicalquantityformeasuringtheworkcapabilityofelectricfieldforcetoelectricchargeinwhichtheelectricfieldforcedrivesthemovementofpositivecharge.ThevoltagebetweenpointsAandBinthecircuitinvalueequalstheworkofelectricfieldforcemovingpositiveunitchargefrompointAtopointB.IfthequantityofelectricchargemovedbytheelectricfieldforceisQandtheworkisW,thevoltagebetweenthetwopointsisasfollows:功（能量）W-焦（耳）（J）Work(energy)W-joule(J)电荷Q-库（仑）（C）ElectricchargeQ-coulomb(C)电压U-伏（特）（V）VoltageU-volt(V),电源电动势ElectromotiveForceofthePowerSupply,正电荷从电源的正极流出，经过电阻R，最后流回负极，这是电场力推动正电荷做功的结果。为了在电路中保持持续的电流，就必须使正电荷从电源负极，经电源内部（称为内电路），移动到电源正极。这时在电源内部存在某种非电场力，例如干电池内部因化学作用而产生的化学力，这种非电场力又称为电源力。它能够把正电荷自电源的负极经过电源内部移动到正极，在这个过程中，是电源力克服电场力对正电荷做功，电源把其他形式的能量转换成为电能。为了衡量电源力对正电荷做功、把其他形式的能量转换成为电能的能力，引人了电动势的概念。Positivechargeoutflowsfromtheanodeofthepowersupply,flowsthrougharesistorRandflowsbacktothecathodefinally.Thisresultsfromdrivingthepositivechargetoworkbytheelectricfieldforce.Tomaintaincontinuouscurrentinthecircuit,thepositivechargemustflowfromthecathodeofthepowersupplytotheanodethroughinsideofthepowersupply(internalcircuit).Non-electricfieldforcesuchaschemicalforceduetochemicalactioninsidethedrybatteryexistsinsidethepowersupplyatthistimeanditisfurthercalledpowersupplyforce.Thisforcecanmovethepositivechargefromthecathodeofthepowersupplytotheanodethroughinsideofthepowersupply.Duringthisprocess,thepowersupplyforceappliesworkonthepositivechargeagainsttheelectricfieldforceandthepowersupplyconvertsenergyofotherformsintoelectricalenergy.Tomeasurethecapabilityofpowersupplyforceofapplyingworkonthepositivechargeandconvertingenergyofotherformsintoelectricalenergy,theconceptofelectromotiveforceisintroduced.,Fig.1-2-5Electromotiveforceofthepowersupply,.,6,电阻Resistance,线性电阻元件的伏安特性遵循欧姆定律。其伏安特性曲线表明，通过电阻元件的电流I与作用在其二端的电压U成正比。当取关联参考方向时（图l33），欧姆定律表示为Volt-amperecharacteristicsoflinearresistiveelementfollowOhmslaw.Itsvolt-amperecharacteristiccurveindicatesthecurrentIoftheresistiveelementisindirectproportiontothevoltageUatbothendsoftheresistiveelement.Whenassociatedreferencedirectionistaken(Fig.1-3-3),theOhmslawisrepresentedas:,式中Where,I导体中的电流（A）；Icurrent(A)intheconductor;U导体两端的电压（V）；Uvoltage(V)atbothendsoftheconductor;R电阻元件的电阻，它定量表示出电阻元件对电流阻碍作用的大小。在国际单位制中，电阻R的单位是欧姆（）。Rresistanceoftheresistiveelement,whichrepresentstheinhibitionoftheresistiveelementtothecurrent.InInternationalSystemofUnits,theunitofresistanceRisohm().,.,7,电位ElectricPotential,电位ElectricPotential1.定义：Definition:电路中某一点的电位就是该点到参考点的电压。Theelectricpotentialatsomepointinthecircuitisthevoltagefromthatpointtothereferencepoint.2.参考点：Referencepoint:参考点的电位为零。Theelectricpotentialofthereferencepointis0.电位参考点所在的导线常称为“地线”，电位参考点的图形符号如图。在电路分析中，通常选取多条导线的交汇点作为电位参考点。以图111l所示电路为例取d点作为电位参考点，则Vd0。Theconductingwire,onwhichthereferencepointofelectricpotentialislocated,isgenerallycalledas“earthwire”.Seethefollowingfigureforgraphicsymbolsofthereferencepointofelectricpotential.Incircuitanalysis,theintersectionofmultipleconductingwiresisgenerallyselectedasthereferencepointofelectricpotential.TakingthecircuitshownintheFig.1-11-1asanexample,thepointdisconsideredasthereferencepointofelectricpotential,andVd0.,Fig.1-11-1Calculationofelectricpotential,.,8,电位的优点：能够使表示电路状态的电量大为减少，这在调试、检修电器设备和电子电路时有实用意义。例如对本电路，如果用电压表示电路的状态一共有6段电压（Uab、Ubc。UcdUac、Uad、Ubd）。若用电位表示，只需要a、b、c点的电位Va、Vb、Vc三个电量就可以了。因为Va、Vb、Vc确定后，各段电压也就随之确定了。在实际检测电路时只需将数字电压表的黑表笔放在电位参考点，然后用红表笔依次接触a、b、c三点，测量出这三点的电位就可以了，非常方便，如图l112所示。Advantagesofelectricpotential:itcanlargelyreducetheelectricquantitiesrepresentingthecircuitstatus,whichhaspracticalsignificanceincommissioningandservicingelectricalequipmentandelectroniccircuits.Forinstance,ifvoltageisusedtorepresentthestatusofthecircuit,thiscircuithas6voltages(Uab,Ubc,Ucd,Uac,UadandUbd).Ifelectricpotentialisapplied,onlythreeelectricquantitiesareenough,whichareelectricpotentialVa,VbandVcatpointsa,b,andc;thevoltagescanbedeterminedafterdeterminingVa,VbandVc.Whenpracticallydetectingthecircuit:puttheblackprobeofdigitalvoltmeteronthereferencepointofelectricpotential,andthenusetheredprobecontactpointsa,bandcsuccessively,soastomeasuretheelectricpotentialatthethreepoints,whichisveryconvenient,asshowninFig.1-11-2.,Fig.1-11-2Measurementofelectricpotential,.,9,电容Capacitance,电容元件CapacitiveComponent电容元件是表示电路中储存电荷，建立电场，储存电场能这一电磁现象的理想电路元件。Thecapacitivecomponentreferstotheidealcircuitelementforstoringcharge,establishingelectricfield,andstoringtheelectricfieldenergy(anelectromagneticphenomenon).（I）电容器Capacitor1.电容器的结构Structureofthecapacitor电容器是一种常用的电子元件或电工设备，它的品种、规格很多。但是就其基本结构而言，都是由两块金属极板被介质隔开构成，常用的介质有陶瓷、云母、电解质、绝缘纸和空气等。电容器的基本结构示意如图1-12-1（a）所示，图（b）所示是几种常用的电容器外形。Thecapacitorisacommonelectronicelementorelectricalequipment,withmultipletypesandspecifications.However,itsbasicstructureisgenerallycomposedoftwometalpolarplates,whichareseparatedbymedium.Commonmediummaybeceramic,mica,electrolyte,insulationpaper,air,etc.SeeFig.1-12-1(a)forbasicstructureofthecapacitor.SeeFig.(b)foroutlinesofseveralcommoncapacitors.,Metallizedpapercapacitor,Micacapacitor,.,10,变压器Transformer,变压器是一种静止的电器设备，它能将某一种电压数值的交流电变换为同频率的另一电压数值的交流电。除了变换电压之外，变压器还具有变换电流、变换阻抗的作用，主要用于输电、配电领域。Transformerisakindofstaticelectricalequipment,whichcantransformanalternatingcurrentofavoltageintoanalternatingcurrentofanothervoltagewiththesamefrequency.Inadditiontotransformingvoltage,thetransformeralsocantransformcurrentandresistance,whichismainlyappliedinpowertransmissionanddistribution.,变压器结构：变压器由铁心和绕在铁心上的两个或多个线圈（又称绕组）组成。Structureoftransformer:thetransformeriscomposedofironcoreandtwoormorecoils(alsoknownaswindings)whichwindtheironcore.铁心的作用是构成变压器的磁路。为了减小涡流损耗和磁滞损耗，铁心采用硅钢片交错叠装或卷绕而成。Theironcoreistoformthemagneticcircuitofthetransformer.Inordertoreduceeddy-currentlossandmagnetichysteresisloss,theironcoreismadeofsiliconsteelsheetsthroughstaggeredoverlaporwinding.根据铁心结构形式的不同，变压器分为壳式和心式两种。如图3-4-1所示。Duetodifferentstructuresofironcores,thetransformerisdividedintoshelltypetransformerandcoretypetransformer,asshowninFig.3-4-1.,心式变压器特点是线圈包围铁心，功率较大的变压器多采用此结构。壳式变压器则是铁心包围线圈，其特点是可以省去专门的保护包装外壳。Thestructureofthecoretypetransformeris:ironcoreissurroundedbycoils,anditisgenerallyappliedintransformerswithlargepower.Thestructureoftheshelltypetransformeris:coilissurroundedbyironcores,whereinspecialprotectingcasingcanbeomitted.,(a)Coretypetransformer,(b)Shelltypetransformer,Fig.3-4-1Structureoftransformer,.,11,图3-4-2画出了一个单相双绕组变压器的原理结构示意图及其图形符号。两个绕组中与电源相连接的一方称为一次绕组，又称原方绕组或初级绕组。凡表示一次绕组各量的字母均表注下标“1”，如一次绕组电压U1、一次绕组匝数N1。与负载相连接的绕组称为二次绕组，又称副方绕组或次级绕组。凡表示二次绕组各量的字母均标注下标“2”，如二次绕组电压U2、二次绕组匝数N2、。变压器二次绕组电压高于一次绕组电压的是升压变压器；反之是降压变压器。Fig.3-4-2showstheprinciplestructurediagramofasingle-phasetwo-windingtransformeranditsgraphicsymbols.Inthetwowindings,thewindingconnectedtothepowersupplyiscalledastheprimarywinding.Lettersrepresentingtheparametersoftheprimarywindingarewithsubscript“1”,forinstance,thevoltageoftheprimarywindingisU1,thenumberofturnsofprimarywindingisN1Thewindingconnectedtotheloadiscalledassecondarywinding.Lettersrepresentingtheparametersoftheprimarywindingarewithsubscript“2”,forinstance,thevoltageofthesecondarywindingisU2,thenumberofturnsofsecondarywindingisN2Thetransformerwhosesecondarywindingvoltageishigherthantheprimarywindingvoltageisstepuptransformer,otherwiseitisstepdowntransformer.,ACsupply,Load,Fig.3-4-2Structurediagramofatwo-windingtransformeranditsgraphicsymbols,.,12,3、汽车起重机电气符号认识KnowledgeofElectricalSymbolsofAutomobileCrane,目录Contents,1、电路模型CircuitModel,2、电路原理PrincipleofCircuits,.,13,开路OpenCircuit,2.开路的特点Characteristicsofopencircuit（1）电路电流为零。Thecircuitalcurrentis0.（2）电源不向负载提供功率，所以又称为空载状态。Thepowersupplydoesnotsupplypowertotheload.Therefore,itcanalsobecalledasno-loadstatus.（3）负载一侧电压U0。电源一侧电压UE，利用这个特点可以用电压表测量电源的电动势。ThevoltageUattheloadsideequalsto0.ThevoltageUatthepowersupplysideequalstoE,onbasisofwhichtheelectromotiveforceofthepowersupplycanbemeasuredbyavoltmeter.,1.开路状态Statusofopencircuit当负载不用电或者检修电源等设备以及排除电路故障时，都需要把负载与电源隔开，如图162所示，负载与电源之间用闸刀开关隔开。电路的这种状态称为开路，又称断路。Incasetheloadispoweredoff,orequipmentsuchaspowersupplyisserviced,andtroubleshootingforcircuitiscarriedout,theloadshouldbedisconnectedtothepowersupplyviaaknifeswitch,asshowninFig.1-6-2.Suchstatusofcircuitiscalledasopencircuit.,Powersupply,Load,Fig.1-6-2Statusofopencircuit,.,14,短路ShortCircuit,短路状态：从广义上说电路的任何一部分被电阻等于零的导线连接起来，使该两端电压等于零，这种现象就称为短路。图l63所示是电源两端被短路的情况。Statusofshortcircuit:inabroadsense,anypartofthecircuitisconnectedtoaconductingwirewitharesistanceof0,whichmakesthevoltageatbothendsis0,suchphenomenoniscalledasshortcircuit.Fig.1-6-3showsshortcircuitatbothendsofthepowersupply.,Fig.1-6-3Statusofshortcircuit,.,15,短路Shortcircuit,短路的特点Featuresofshortcircuit（1）端电压U0，故流过负载的电流I0。TerminalvoltageU0,thusthecurrentflowingthroughtheloadI0.（2）负载吸收的电功率为零。Thepowerabsorbedbytheloadiszero.（3）短路电流Iac很大。此时流过电源的电流Isc=E/RO，称为短路电流。通常电源的内阻RO总是很小的，所以短路电流Iac很大，可能是正常工作电流的几十倍，甚至更大。Theshort-circuitcurrentIacisverystrong.ThecurrentflowingthroughthepowersupplyIsc=E/RO,namely,theshortcircuit.Usually,theinternalresistanceofthepowersourceROisverysmall,thusleadingtoaverystrongIac,probablydozensoftimesofthenormalcurrentorevenbigger.（4）电源产生的电功率P全部消耗在内阻Ro上，此时PI2RO，因此会产生大量热量，造成人员伤害或设备损坏，是一种严重的事故，应尽力避免。为此要在电路上加装保护电器，如熔断器。Allofthepowerproducedbythepowersupply(P)isconsumedbytheinternalresistanceRoandPI2RO;itwillproducealargeamountofheatcausingpersonalinjuryorequipmentdamage,whichisaseriousaccidentandshouldbeavoidedaspossiblyasonecando.Forthispurpose,aprotectivedevicesuchasafuseshouldbearrangedonacircuit.,.,16,负载工作状态Workingstatusoftheload,电源与负载接通，电源向负载提供电功率，这种状态就是负载工作状态。图l65所示。Theworkingstatusoftheloadissuchthatthepowersupplyisconnectedwithandprovidespowerfortheload,asisshowninFig.l65.,电源Powersupply图1-6-5负载工作状态Fig.1-6-5Workingstatusoftheload,.,17,2.特点Features（1）由电路图可得电流为Basedonthecircuitdiagram,thecurrentisdeterminedas（2）电源的端电压，即负载电压为UIR=EIROTerminalvoltageofthepowersupply,namelytheloadvoltageUIR=EIRO（3）功率转换关系：Transformationalrelationofthepower:电压平衡方程E=IROIRVoltagebalanceequation:E=IROIR功率平衡方程EI=I2RO+I2RPowerbalanceequation:EI=I2RO+I2R上式表明，电源产生的总电功率P总EI，是电源内阻凡和负载R吸收的电功率之和满足功率平衡关系。TheaboveformulasindicatethatthetotalpowerproducedbythepowersupplyPtotalEI,whichisthesumofthepowerabsorbedbytheinternalresistanceofthepowersupplyandthatbytheload(R).负载吸收的电功率：PR=I2R电源输出的电功率：PEII2RO(PR=P)Powerabsorbedbytheload:PR=I2R;outputpowerofthepowersupply:PEII2RO(PR=P),.,18,串联分压Voltagedivisioninseries,串联电阻的分压作用Voltagedivisionoftheresistancesinseries以两个电阻串联电路。两个电阻的端电压分别是Tworesistancesarearrangedinseriesonthecircuit;thetwoterminalvoltagesare:U1、U2是总电压U的一部分，且U1、U2分别与阻值R1、R2成正比。即阻值大的电阻承受的电压较高。U1andU2arepartialvoltagesofthetotalvoltageUandareindirectionproportiontoR1andR2,namely,thelargerresistancebearsahighervoltage.串联电阻的分压作用在实际电路中有广泛应用，如电压表扩大量程、电子电路中的信号分压。衰减网络、直流电动机的串联电阻起动等。Thevoltagedivisionofresistancesinseriesiswidelyusedinpracticalcircuitssuchasexpandingofthevoltmeterrange,voltagedivisionofsignalsontheelectroniccircuitandstartofresistancesinseriesofattenuationnetworkandDCmotor.,.,19,并联分流Currentdivisioninparallel,图1-7-9两个电阻的并联电路Fig.1-7-9:Acircuitwithtworesistancesinparallel,并联电阻的分流作用Currentdivisionofresistancesinparallel现以图1-79所示两个电阻的并联电路为例来分析说明。AcircuitwithtworesistancesinparallelshowninFig.1-7-9isdemonstratedforanalysis.,上式表明，支路电流I1、I2人都是总电流I的一部分，对总电流I有分流作用，且阻值较小的支路分流较多。以上公式都是常用公式，应该熟记。TheaboveformulasindicatethatthebranchcurrentsI1andI2arepartialtothetotalcurrentIandbothcontributetodividethetotalcurrentwiththesmallerresistancedividingalargercurrent.Thesearecommonly-usedformulasandshouldbelearntbyheart.并联电阻的分流作用在工程技术中也有广泛应用。Thecurrentdivisionofresistancesinparallelisalsowidelyappliedintheengineeringtechnology.,.,20,电流测量方法Measuringmethodofcurrent,a)测量电流时，电流表应直接串联接入被测电路，如图1132所示。为了不使因电流表串入而影响被测电路，电流表的内阻必须很小。Incaseofcurrentmeasuring,theamperemetershouldbedirectlyconnectedwiththemeasuredcircuitinseries,asisshowninFig.1-13-2.Theinternalresistanceoftheamperemetershouldbeextremelysmallsoasnottoaffectthemeasuredcircuit.b)将直流电流表接入电路要注意电流表的极性：使电流自电流表的正极性端（通常标注红色或“”）流入，从电流表负极性端（通常标注黑色或“”）流出。如接错，指针将反向偏转，可能损坏电流表。PayattentiontoitspolaritywhenconnectingtheDCamperemeterintothecircuit:tomakethecurrentflowinfromthepositivepolarity(usuallyindicatedwithredor“+”)of